Thunder god vine, a woody vine of Celastraceae Tripterygium, is distributed at the south of Yangtze River or southwest region. It is cold in nature, bitter and toxic. Triptolide (TP) is an epoxidized diterpene lactone compound separated from a traditional Chinese medicine Tripterygium wilfordii Hook f, and is one of the main active ingredients in T. wilfordii Hook f Triptolide is in the form of white crystals. It is not soluble in water but soluble in various organic solvents.

Triptolide is a diterpenoid compound with an abietane skeleton. It has three epoxy structures and an α,β-unsaturated five-membered lactone ring. Triptolide has various activities such as anti-inflammatory, immunosuppressive, anti-fertility and anti-cancer activities. It can be used to treat rheumatoid arthritis, systemic lupus erythematosus, ankylosing spondylitis and cancer etc. Studies show that triptolide is a broad-spectrum cancer suppressor and can induce apoptosis of a variety of cancers cell in in vitro, including ovarian cancer, breast cancer, colon cancer, oral cancer, stomach cancer and so forth. It can also inhibit tumor growth and metastasis of cancer cells in vivo, including hematological cancers, malignancies and solid cancers. The anti-cancer activity of triptolide is better than that of the traditional anti-cancer drugs such as cisplatin, doxorubicin and paclitaxel. Triptolide can effectively inhibit the growth of the cancer cells at an extremely low concentration (2-10 ng/ml). Further, triptolide can overcome the drug resistance of cancer cells and at the same time increases the sensitivity of cancer cells to other anti-cancer drugs. Triptolide further has synergistic effect when combining with chemotherapeutic drugs and ionizing radiation.
Currently, many studies have focused on investigating the anti-cancer mechanism of triptolide. Triptolide can inhibit the expression of heat shock protein 70 (HSP 70). As an inhibitor of heat shock protein response, triptolide can effectively inhibit the expression of HSP 70 genes and induce cell apoptosis. Triptolide can inhibit nuclear factor kappaB (NF-κB, NF-κB does not only promote cancer cell proliferation but also activate oncogene and anti-apoptotic genes) which lowers the sensitivity of cancer cells towards apoptosis. In one hand, triptolide inhibits the combination of NF-κB and a specific DNA sequence at the target gene and further interferes the transcription activity of NF-κB; on the other hand, triptolide can prevent nuclear kinase from performing phosphorylation on NF-κB trans-activating region or interfere the nuclear accumulation of auxiliary protein of NF-κB, i.e. cAMP response element binding protein, as well as interfere the interaction between P65 and RNA polymerase and further inhibits the transcription activity of NF-κB to promote apoptosis. In addition to the above mechanism, triptolide can further exhibit its anti-cancer effect through various ways such as inhibiting ubiquitin-proteasome, affecting the activity of RNA polymerase, affecting the expression of p53 gene, activating caspase etc. Thus, triptolide is a potent candidate of anticancer drug.
Although triptolide has significant anti-tumor activity, the low bioavailability due to its poor water solubility and the high toxicity limit its clinical application.
Researchers of the technical field have modified the structure of triptolide, and some of the studies show that:
1. When C14 hydroxyl is replaced by an electron withdrawing group, the cytotoxicity of the derivatives increases, as shown in FIG. 1-1; the cytotoxicity of M-1 and M-2 are greater than TP, however, the activity of M-1 is greater than M-2, i.e. the steric effect at C-14 is significant.

2. When C14 hydroxyl forms a structure of three-membered epoxy, the bioactivity increases and the toxicity decreases because it cannot form intra-molecular hydrogen bond. However, when it forms a five-membered ring, the activity decreases. This may be because of the steric effect which causes the combination of the receptor and the drug, as shown in FIG. 1-2.

3. When epoxy at C12,13 position opens the ring structure, the formed structure has a certain stability in vivo and that the immunosuppressive activity of such a derivative is diminished while the anti-inflammatory activity remains unchanged. Epoxy at C7,8 is less susceptible to nucleophilic attack, however, the bioactivity and the cytotoxicity of the derivative formed after the ring-opening decrease. There are few reports regarding ring-opening of epoxy at C12,13 position, nevertheless, the bioactivity of the derivative formed after the ring-opening does not vary significantly, as shown in FIG. 1-3:

4. α,β-unsaturated five-membered lactone ring is one of the essential groups for exhibiting bioactivity. Modifications to the lactone ring significantly reduce the activities of the compound, such as anti-cancer activity and immunosuppressive activity. Although the modification to C5 position results in cytotoxicity and reduces the immunosuppressive activity, the derivative still has good in vivo and in vitro activities with significantly reduced toxicity. Accordingly, the safety of the treatment is greatly improved, as shown in FIG. 1-4.

To conclude, current modifications to triptolide mainly include C14 hydroxyl, α,β-unsaturated five-membered lactone ring, C12,13 epoxy, C7,8 epoxy and C9,11 epoxy. The β-OH at C14 position is the only nucleophilic group in the molecule, which is associated with the water solubility and cytotoxicity of triptolide. This β-OH can form intra-molecular hydrogen bond with β-epoxy at C9,11 position and is the critical group of anti-cancer effect. When β-OH at C14 is replaced by an electron withdrawing group, the cytotoxicity of the derivatives increases; when β-OH at C14 forms a three-membered epoxy, it cannot form intra-molecular hydrogen bond, and thus the bioactivity increases while the toxicity decreases. The epoxy structure at C12,13 position has a certain stability in vivo after the ring-opening. The derivatives formed after the ring-opening still possess the anti-inflammatory activity but not the immunosuppressive activity. When the epoxy structure at C7,8 opens, the bioactivity and cytotoxicity decrease. α,β-unsaturated five-membered lactone ring is an essential group, and the modifications to the lactone ring can reduce the bioactivities of the derivative, such as anti-cancer activity and immunosuppressive activity. However, the modified derivatives still have good effects with significantly reduced toxicity. Accordingly, the safety of the treatment is greatly improved.
The modification sites on triptolide mainly include hydroxyl at C14, epoxy at C12,13, α,β-unsaturated five-membered lactone ring, epoxy at C7,8 and epoxy at C9,11. However, among the modified triptolides, only those compounds having modification on the hydroxyl at C14, epoxy at C12,13, and carbonyl at C18 can be converted to triptolide in vivo and then exert its therapeutic effect.
Aptamer is a kind of oligonucleotides with therapeutic effects. It can bind with target proteins with high affinity and selectivity, and its function is similar to a monoclonal antibody. There are many advantages of aptamers in practice: high affinity and high selectivity; small molecular weight and therefore aptamers can enter the cell through cell membrane, and can be readily directed to the in vivo target site with a substantial amount; good stability and the half-life is long in vivo; they are not sensitive to the ambient temperature and thus it is easy to store; it is easy to synthesize and modify, and therefore improve the applications of aptamers in clinical diagnosis and treatments. Aptamers can be directly used as drugs for treating diseases. When part of the aptamers binds to the corresponding target sequence, the function of the respective protein is inhibited as the binding site represents the functional region of the protein. Aptamers can also be used as drug carriers. The connection between the drug and the aptamers render the drug to have cell selectivity so as to avoid toxic side effects to normal tissues and cells.
AS1411 and Sgc8c are well-known aptamers. AS1411 is a guanine rich oligonucleotide (GROs) and can form a stable G-quadruplex structure. The nucleotide sequence of AS1411 is consisting of SEQ ID NO: 1 and can effectively act against intracellular nuclease degradation. AS1411 can specifically binds to nucleolin highly expressed on the surface of the cancer cell, and nucleolin on the cell membrane enhances great pinocytosis of the cancer cell to AS1411 and thus increase the uptake. A number of studies showed that AS1411 has broad-spectrum anti-cancer activity. The study on the anti-proliferative activity of AS1411 on a variety of human cell lines show that AS1411 is capable of inhibiting almost all kinds of cancer cells, IC50 reaches micro molar level and such a concentration has weak impact to normal cells. The anti-cancer mechanism of AS1411 mainly involves the inhibition of the cellular DNA replication after entering the nuclear, so as to arrest the cell cycle in S-phase, thereby inhibiting cancer cell proliferation. Sgc8c is a single-stranded DNA aptamer specifically targeting T-cell acute lymphoblastic leukemia. Sgc8c was screened by systematic evolution of ligands by exponential enrichment (cell-SELEX) using intact cells as target enrichment index. Since Sgc8c has many advantages such as high stability in serum, high specificity and low immunogenicity, it is used as the target ligand for coupling with chemotherapeutic agents and achieves an excellent result in the treatment of T-cell acute lymphoblastic leukemia. The nucleotide sequence of Sgc8c is consisting of SEQ ID NO: 2.
However, there are no reports of improving the biological performances of triptolide and its structural derivatives by combining triptolide and its structural derivatives with aptamers.